Abstract
Purpose: A new linker, hydrazino nicotinamide (HYNIC), was recently introduced for labelling of liposome with $^{99m}Tc$. In this study we synthesized HYNIC derivatized PEG (polyethylene glycol)-liposomes radiolabeled with $^{99m}Tc$. Materials and Methods: In order to synthesize HYNIC-DSPE (distearoyl phosphatidyl ethanolamine) which is a crucial component for $^{99m}Tc$ chelation, first of all succinimidyl 6-BOC-hydrazinopyridine-3-carboxylic acid was synthesized from 6-chloronicotinic acid by three sequential reactions. A DSPE derivative of succinimidyl 6-BOC-hydrazinopyridine-3-carboxylic acid was transformed into HYNIC-DSPE by HCI/dioxane. HYNIC-PEG-liposomes were prepared by hydration of the dried lipid mixture of EPC (egg phosphatidyl choline): PEG-DSPE : HYNIC-DSPE:cholesterol (1.85:0.15:0.07:1, molar ratio). The HYNIC-PEG-liposomes were labeled with $^{99m}Tc$ in the presence of $SnCl_2{\cdot}2H_2O$ (a reducing agent) and tricine (a coligand). To investigate the level of in vivo transchelation of $^{99m}Tc$ in the liposomes, the $^{99m}Tc$-HYNiC-PES-liposomes were incubated with a molar excess of DTPA, cysteine or glutathione solutions at $37^{\circ}C$ for 1 hour. The radiolabeled liposomes were also incubated in the presence of human serum at $37^{\circ}C$ for 24 hours. Results: 6-BOC-hydrazinopyridine-3-carboxylic acid was synthesized with 77.3% overall yield. The HYNIC concentration in the PEG-coated liposome dispersion was 1.08 mM. In condition of considering the measured liposomal size of 106 nm, the phospholipid concentration of $77.5\;{\mu}mol/m{\ell}$ and the liposomal particle number of $5.2{\times}10^{14}$ liposomes/ml, it is corresponded to approximate 1,250 nicotinyl hydrazine group per liposome in HYNIC-PEG-liposome. The removal of free $^{99m}Tc$ was not necessary because the labeling efficiency were above 99%. The radiolabeled liposomes maintained 98%, 96% and 99%, respectively, of radioactivity after incubation with transchelators. The radiolabeled liposomes possessed above 90% of the radioactivity in serum. Conclusion: These results suggest that the HYNIC can be synthesized easily and applied in labelling of PEG-liposomes with $^{99m}Tc$.
목적: BFCA 중 하나인 HYNIC을 제조하고, 염증부위에 선택적으로 국소화 되어 진단할 수 있는 PEG-liposome과 결합시켜 HYNIC-PEG-liposome을 제조하며, 제조된 HYNIC-PEG-liposome에 방사성 동위원소인 $^{99m}Tc$의 표지 방법을 확립하고자 하였다. 대상 및 방법: 6-Chloronicotinic acid를 출발물질로 하여 succinimidyl 6-BOC-hydrazinopyridine-3-carboxylic acid를 순차적으로 합성하였다. Triethylamine을 이용해 합성된 succinimidyl 6-BOC-hydrazinopyridine-3-carboxylic acid와 DSPE를 접합하였다. HYNIC-DSPE를 제조한 후에 EPC:PEG-DSPE: HYNIC-DSPE:cholesterol을 1.85:0.15 :0.07:1의 몰 비로 혼합하여 HYNIC-PEG-liposome을 제조하였다. 제조된 HYNIC-PEG-liposome에 $SnCl_2{\cdot}2H_2O$와 tricine을 이용하여 $^{99m}Tc$를 표지하였다. $^{99m}Tc$-HYNIC-PEG-liposome과 혈청을 섞어서 실온과 $37^{\circ}C$에서 24시간까지 안정성을 확인하였다. $^{99m}Tc$-HYNIC-PEG-liposome에 DTPA, cysteine, glutathione을 각각 과량의 몰 비로 섞고 $37^{\circ}C$에서 1시간 반응 후에 trans- chelation을 통해 안정성을 확인하였다. 결과: 6-Chloronicotinic acid를 출발물질로 하여 6-hydrazinopyridine-3-carboxylic acid, 6-BOC-hydrazinopyridine -3-carb-oxylic acid, succinimidyl-6-BOC-hydra-zino-pyri- dine-3-carboxylic acid를 합성하였으며 각각의 합성수율은 88.5%, 93.7%, 93.2%였고 최종수율은 77.3%였다. 제조된 HYNIC-PEG-liposome의 직경은 106 nm였고, PEG-liposome에 접합된 HYNIC의 농도는 1.08 nM이었다. HYNIC-PEG- liposome의 개수는 1 ml에 $5.2{\times}10^{14}$개가 존재하였고, PEG- liposome 한 개당 HYNIC은 약 1250개가 접합되었다. 제조된 HYNIC-PEG-liposome에 $SnCl_2{\cdot}2H_2O$와 tricine을 이용하여 $^{99m}Tc$를 표지하였으며 그 표지수율은 99%이상이었다. 혈청 내에서 24시간까지 93.5% 이상의 안정성을 나타내었다. DTPA, cysteine, glutathione을 각각 1000배의 몰 비를 첨가한 경우 $^{99m}Tc$-HYNIC- PEG-liposome의 방사화학적순도가 각각 98%, 96%, 99%으로서 안정하였다. 결론: BFCA중 하나인 HYNIC을 이용한 $^{99m}Tc$-HYNIC-PEG-liposome의 제조는 손쉬운 표지방법과 높은 표지수율 그리고 안정성을 나타낼 수 있는 방법으로서, 이를 염증부위에 선택적으로 국소화되어 염증의 진단에 유용하게 사용될 수 있을것으로 기대된다.